1. Field of the Invention
The present invention relates to an apparatus for estimating vibration input to a suspension device of a vehicle.
More particularly, the invention pertains to an apparatus for estimating a vibration input to be transferred to the suspension device from a road surface, which is suitable for a suspension control system adapted to perform a predict control of an actuator which is arranged between a wheel to be controlled and the body work of the vehicle, on the basis of a road surface information detected on the front side of the wheel to be controlled.
2. Description of the Prior Art
An apparatus for estimating a vibration input to a suspension device is disclosed, e.g., in JP-A-61-166715, wherein an acceleration sensor is arranged on a suspension arm of a front wheel, for detecting a vertical acceleration generated by a front wheel motion in a direction perpendicular to a road surface, and changing the suspension characteristic of a rear wheel on the basis of the vertical acceleration value. However, since the acceleration sensor for detecting the vertical acceleration is arranged on the suspension arm, it is difficult to implement the apparatus in effect due to insufficient durability and weatherproofness of the sensor itself. Furthermore, it is also difficult to accurately detect the vertical acceleration of the wheel alone, due to a vertical motion of the body work which is transferred to the suspension device.
Another type of apparatus for estimating a vibration input to a suspension device is disclosed, e.g., in JP-A-61-135811, which is combined with a shock absorbing system of a vehicle having wheels driven to rotate along a road surface, and a spindle mechanism for supporting the wheel and the body work. The spindle mechanism is driven at a predetermined interval in response to roughness of the road surface. The apparatus includes a detector comprising an ultrasonic probe which is arranged on the front side of the front wheel and detects the roughness of the road, a controller which instructs expansion or contraction of spindle mechanism according to the signal of the detector and a running speed signal, and a valve driving mechanism for exciting an electromagnetic valve to charge or discharge hydraulic oil into or from the spindle mechanism according to the instruction. However, since the ultrasonic probe is used as a non-contact type sensor for detecting a road surface roughness, measurement error is liable to be caused by snow, puddles and the like. It is furthermore difficult to select only the roughness data of the road surface from the measurement data in which vibration data of the body work also is included due to the arrangement of the sensor on the body work.